With control of the United States Senate looking like a toss-up, the next vice president could end up holding the balance of power.
A Donald Trump victory on Tuesday would likely correspond with Republicans holding on to the Senate. Democrats need to flip five seats to take control. Flipping four seats means Republicans and Democrats will be tied at 50 each.
In a year with a half-dozen strong swing states, that's looking increasingly plausible. If that happens and Hillary Clinton wins, her running mate Tim Kaine would become one of the most powerful people in America and the key to getting any of Clinton's nominees or legislative priorities through the Senate.
When the Senate ties it turns to the vice president — who sits as the president of the Senate — to break the tie.
Republicans currently hold 7 of the 12 contested Senate seats with the tightest races heading into Tuesday's election in North Carolina, New Hampshire, Indiana, Missouri, Pennsylvania, and Nevada. If Democrats can gain four of those seats, they'll have a tie.
Should Clinton take the White House as well, Tim Kaine would then be the key to a Democratic Senate majority.
This hasn't happened recently. Joe Biden didn't break a single tie during Obama's term. But it has happened 244 times in American history, most recently by Dick Cheney in 2008.
The vice president who broke the most ties was the very first one, John Adams, with 29 deciding votes.
In the event of an electoral college tie of 269, the incumbent House of Representatives selects the president while the Senate selects the vice president.
With Republicans currently controlling both chambers of Congress, that means Trump and Mike Pence would be appointed. A tie has only happened once in history — the election of 1800, when the House ultimately awarded Thomas Jefferson the presidency over John Adams.